Debugging Dynamic Memory Usage Errors Using HP WDB (5900-1474; WDB 6.2; January 2011)

Step by Step Approach for Detecting Leaks

This section provides the guidelines and a sample test case to enable you detect memory

leaks by going through a step by step procedure.

Steps to Detect Point of Memory Leak

To detect the point of memory leak, ensure that you go through following steps:

1. Enable memory leak detection for the application run and collect the leak report in

batch mode. To enable leak detection, use check_leaks=on in the rtcconfig

file.

2. The batch mode run reports memory leaks. From this report, pick up the leaks one

by one and detect the point of leak following the instructions below. Run the

application under gdb with the -leaks command.

3. Detect the location of memory leak using the steps mentioned below.

a. Insert a breakpoint at the function that allocates the memory. Step into the calling

function using the finish command and collect leak information with the info

leaks command after the execution reaches the calling function.

NOTE: If the address of the allocated memory location is in a register or if the

address is in RSE contents, then the leak information is not shown and henceforth

means that some data in the program still points to the allocated memory.

b. Continue the previous step and step into the next calling function in the stack

trace and collect leak information with the info leaks command after the

execution reaches the next calling function. If a leak information is displayed,

then you can infer that the pointer to the allocated memory is lost before getting

into the function or in the function.

c. Find the statement causing the loss of this pointer to the allocated memory in

caller of the current function or in the current function.

Sample Test Case to Detect Point of Memory Leak

The “Steps to Detect Point of Memory Leak” (page 89) are represented through a sample

test case. The sample test case is provided as shown below:

1 #include <stdio.h>

2 #include <string.h>

3 #include <stdlib.h>

5 /* Allocate memory and return it to the caller */

6 void *allocateMemory(size_t n)

7 {

8 void *memBlock = NULL;

9 printf("Allocating memory of size %d\n", n);

11 memBlock = malloc(n);

12 if (!memBlock)

13 {

Step by Step Approach for Detecting Leaks 89